1. Field of the Invention
The present invention relates to a sheet ejection tray onto which sheets having images formed thereon are ejected from an image forming apparatus and stacked.
2. Description of the Related Art
In order to respond to a need of reducing the thickness of sheets used for contents in an envelope and the like, for example, thin sheets are provided as a type of sheets used in the image forming apparatus. Since the thin sheets are not sturdy, leading ends of the sheets might be lifted up or rolled by air resistance received from the peripheral air when being ejected onto a sheet ejection tray. Such a phenomenon is particularly remarkable during high-speed printing when the sheets are conveyed at a high speed. Thus, sheet alignment of the ejected sheets on the sheet ejection tray and the like are adversely affected.
Conventional proposals for improving sheet alignment when thin sheets are ejected onto the sheet ejection tray include handling of the above-described problem by suspending the leading end of a sheet by using air resistance during sheet ejection, for example. However, if the leading end of the sheet is suspended during ejection, the leading end of the sheet lands on the sheet ejection tray and is caught by the sheet ejection tray before a position where the sheet should have been ejected, and the sheet is ejected onto the sheet ejection tray in a state where the leading end side is rolled inward. Such sheets cause disturbance in alignment of subsequent sheets ejected onto the sheet ejection tray.
Therefore, in the above-described conventional proposal, an inclined surface with inclination larger than that of the sheet ejection tray is provided on the sheet ejection tray. This inclined surface is brought into contact with the suspended leading end of the sheet ejected onto the sheet ejection tray and corrects the direction of the sheet leading end to above a sheet ejection tray surface (Patent Literature 1: Japanese Patent Application Laid-Open Publication No. 2007-55707, for example).
In an image forming apparatus in which a conveying speed of the sheet is increased in accordance with the high-speed printing, a sheet ejecting speed of the sheet with respect to the sheet ejection tray is high, and a distance for which the sheet moves until it lands on the sheet ejection tray becomes longer. Thus, sheet alignment tends to be disturbed by air resistance received by the sheet from the periphery. Thus, in an image forming apparatus adapted to high-speed printing, a sheet landing on the sheet ejection tray is moved so as to return to the base end side of the sheet ejection tray by using the inclination of the sheet ejection tray, and a rear end of the sheet is brought into contact with an abutting cover on the base end of the sheet ejection tray, which is effective in improvement of sheet alignment.
However, if the leading end of the sheet ejected onto the sheet ejection tray is brought into contact with the inclined surface on the sheet ejection tray as in the above-described conventional proposal, when the sheet slides down the inclined surface with inclination larger than that of the sheet ejection tray, the sheet is accelerated, and the rear end of the sheet is brought into contact with the abutting cover in a rush. Then, the rear end side of the sheet is swollen and curved by the rush when the sheet is brought into contact with the abutting cover. Such a sheet causes new disturbance in sheet alignment of the sheets to be subsequently brought into contact with the abutting cover.
The above-described problem often occurs particularly in a thin sheet having a dimension not smaller than a predetermined value in the sheet ejecting direction (feeding direction). On the other hand, since the thin sheet having a dimension less than the predetermined value in the sheet ejecting direction has rigidity higher than that of the thin sheet having a dimension not smaller than the predetermined value, the sheet withstands an impact received by the sheet rear end at contact with the abutting cover and the sheet is not curved. This is considered to be the reason for the above-described problem.
Therefore, even with the sheet having a dimension less than the predetermined value in the sheet ejecting direction when being conveyed with the short side conforming to the feeding direction, if the sheet is conveyed with the long side of the sheet conforming to the feeding direction, the dimension becomes not smaller than the predetermined value in the sheet ejecting direction, and the above-described problem might occur.